如何避免使用 TWebBrowser 刷新

Question

我有一个显示 Google 地图页面的 TWebBrowser 组件。问题是，当用户按 F5 时，页面刷新并重新加载。这会导致 javascript 变量重新初始化并与 Delphi 不同步，并出现脚本错误对话框， “未定义”为空或不是对象。

我想停止用户刷新。

我为 OnBeforeNavigate2 尝试了此事件：

procedure TNewOrganizationForm.mapAddressBeforeNavigate2(ASender: TObject;
  const pDisp: IDispatch; var URL, Flags, TargetFrameName, PostData,
  Headers: OleVariant; var Cancel: WordBool);
begin
  inherited;
  Cancel := Assigned(fMapEngine) and not fMapEngine.Loading;
end;

但是当我设置断点时，它甚至没有被调用。还有别的办法吗？

Answer 1

罗纳德，您可以使用 IHTMLDocument2.onkeydown 事件拦截并阻止按键。

要首先分配事件处理程序，您必须使用 IHTMLEventObj 作为参数。

  THTMLProcEvent = procedure(Sender: TObject; Event: IHTMLEventObj) of object;

那么您必须创建一个从InterfacedObject 和IDispatch 派生的类来传递和处理事件。

最后就可以这样处理onkeydown事件中拦截到的按键

Var
  HTMLDocument2 : IHTMLDocument2;
begin
    if Not Assigned(WebBrowser1.Document) then  Exit;
    HTMLDocument2:=(WebBrowser1.Document AS IHTMLDocument2);
    if HTMLDocument2.parentWindow.event.keyCode=VK_F5 then //compare the key
    begin
     HTMLDocument2.parentWindow.event.cancelBubble:=True; //cancel the key
     HTMLDocument2.parentWindow.event.keyCode     :=0;
    end;
end;

//查看完整源码

unit Unit55;

interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, OleCtrls, SHDocVw, MSHTML;

type
  //Create the procedure type to assign the event
  THTMLProcEvent = procedure(Sender: TObject; Event: IHTMLEventObj) of object;

  //Create a  new class for manage the event from the twebbrowser
  THTMLEventLink = class(TInterfacedObject, IDispatch)
  private
    FOnEvent: THTMLProcEvent;
  private
    constructor Create(Handler: THTMLProcEvent);
    function GetTypeInfoCount(out Count: Integer): HResult; stdcall;
    function GetTypeInfo(Index, LocaleID: Integer; out TypeInfo): HResult; stdcall;
    function GetIDsOfNames(const IID: TGUID; Names: Pointer;
      NameCount, LocaleID: Integer; DispIDs: Pointer): HResult; stdcall;
    function Invoke(DispID: Integer; const IID: TGUID; LocaleID: Integer;
      Flags: Word; var Params; VarResult, ExcepInfo, ArgErr: Pointer): HResult; stdcall;
  public
    property OnEvent: THTMLProcEvent read FOnEvent write FOnEvent;
  end;

  TForm55 = class(TForm)
    WebBrowser1: TWebBrowser;
    procedure FormShow(Sender: TObject);
    procedure WebBrowser1NavigateComplete2(ASender: TObject; const pDisp: IDispatch; var URL: OleVariant);
    procedure FormCreate(Sender: TObject);
  private
    { Private declarations }
    FOnKeyDownConnector:  THTMLEventLink; //pointer to the event handler
    procedure WebBrowser1OnKeyDown(Sender: TObject; EventObjIfc: IHTMLEventObj);//the event handler 
  public
    { Public declarations }
  end;

var
  Form55: TForm55;

implementation

{$R *.dfm}


constructor THTMLEventLink.Create(Handler: THTMLProcEvent);
begin
  inherited Create;
  _AddRef;
  FOnEvent := Handler;
end;


function THTMLEventLink.GetIDsOfNames(const IID: TGUID; Names: Pointer; NameCount, LocaleID: Integer; DispIDs: Pointer): HResult;
begin
  Result := E_NOTIMPL;
end;


function THTMLEventLink.GetTypeInfo(Index, LocaleID: Integer; out TypeInfo): HResult;
begin
  Result := E_NOTIMPL;
end;


function THTMLEventLink.GetTypeInfoCount(out Count: Integer): HResult;
begin
  Result := E_NOTIMPL;
end;


function THTMLEventLink.Invoke(DispID: Integer; const IID: TGUID; LocaleID: Integer; Flags: Word; var Params; VarResult, ExcepInfo, ArgErr: Pointer): HResult;
var
  HTMLEventObjIfc: IHTMLEventObj;
begin
  Result := S_OK;
  if Assigned(FOnEvent) then FOnEvent(Self, HTMLEventObjIfc);
end;



procedure TForm55.FormCreate(Sender: TObject);
begin
  FOnKeyDownConnector := THTMLEventLink.Create(WebBrowser1OnKeyDown); //assign the address of the event handler
end;


procedure TForm55.WebBrowser1NavigateComplete2(ASender: TObject;  const pDisp: IDispatch; var URL: OleVariant);
var
  HTMLDocument2      : IHTMLDocument2;
begin
  HTMLDocument2:=(WebBrowser1.Document AS IHTMLDocument2);
  HTMLDocument2.onkeydown := FOnKeyDownConnector as IDispatch; //assign the event handler
end;

procedure TForm55.WebBrowser1OnKeyDown(Sender: TObject; EventObjIfc: IHTMLEventObj);
Var
  HTMLDocument2 : IHTMLDocument2;
begin
    //finally do your stuff here, in this case we will intercept and block the F5 key.
    if Not Assigned(WebBrowser1.Document) then  Exit;
    HTMLDocument2:=(WebBrowser1.Document AS IHTMLDocument2);
    if HTMLDocument2.parentWindow.event.keyCode=VK_F5 then
    begin
     HTMLDocument2.parentWindow.event.cancelBubble:=True;
     HTMLDocument2.parentWindow.event.keyCode     :=0;
    end;
end;



procedure TForm55.FormShow(Sender: TObject);
begin
WebBrowser1.Navigate('www.google.com'); 
end;



end.

Answer 2

我没有找到一个简单的方法来做到这一点。我在 TWebBrowser 上找不到任何会禁用刷新的事件或类似内容。也许您应该检查 TEmbededWB 因为它比默认的 TWebBrowser 有更多事件并且功能更强大。否则它们非常相似。

但我找到了一种防止刷新的方法。现在有趣的是，即使在主窗体上将 KeyPreview 设置为“True”，我也无法收到关键通知。 TWebBrowser 似乎以某种方式吞噬了它们。但这是有效的：

procedure TForm1.FormCreate(Sender: TObject);
begin
  Application.OnMessage := OnAppMessage;
end;

procedure TForm1.OnAppMessage(var Msg: TMsg; var Handled: Boolean);
begin
  if Msg.message = WM_KEYDOWN then
    if Msg.wParam = VK_F5 then
      Handled := True;
end;

不是最优雅的方式，但至少它有效。我还没有找到更好的解决方案。